Abundance, habitat use and food consumption of seabirds in the high-Arctic fjord ecosystem

Abstract

To monitor the rapid changes occurring in Arctic ecosystems and predict their direction, basic information about the current number and structure of the main components of these systems is necessary. Using boat-based surveys, we studied the numbers and distribution of seabirds foraging in Hornsund (SW Spitsbergen) during three summer seasons. The average number of seabirds foraging concurrently in the whole fjord was estimated at 28,000. Little Auks Alle alle were the most numerous, followed by Northern Fulmars Fulmarus glacialis, Brünnich’s Guillemots Uria lomvia and Black-legged Kittiwakes Rissa tridactyla. The pelagic zone was exploited by some 75% of the birds. Their density was the highest (> 400 ind. km−2) in the tidewater glacier bays, where kittiwakes were predominant, and the lowest in the coastal glacier bays. The seabirds in Hornsund daily consumed c. 12.7 tons of food, i.e. c. 0.2% of the summer mesozooplankton and fish standing stocks available in the fjord. This food consisted primarily of copepods, amphipods and molluscs (c. 70%), whereas fish made up < 15%. More than 50% of this biomass was ingested by pursuit divers, while surface feeders took c. 29% and benthophages c. 13%. About three-quarters of the food biomass was taken from the pelagic zone. This paper describes, for the first time in quantitative terms, the structure and function of a seabird community foraging in an Arctic fjord. It also provides a baseline for future studies on climate-induced changes in the importance of seabirds in the Arctic food web.

Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

“…Only one CTD cast from the same position, measured using the available coordinates, per day was included in the AWI estimation. Even though little auks do not always forage inside the fjords during chick rearing, they are regularly observed there (at least in Hornsund, Stempniewicz et al., 2021a;Stempniewicz et al, 2021b) and generally do short trips to find food for their offspring and use areas located <50 km away from the colony (e.g., Welcker et al, 2009;Jakubas et al, 2020). We thus expect the within-fjord AWI to be representative of the level of "Atlantification" in the foraging areas used by breeding little auks for finding food for their chicks.…”

Molecular tools prove little auks from Svalbard are extremely selective for Calanus glacialis even when exposed to Atlantification

“…Cold waters surrounding Hornsund and Bjørnøya rich in C . glacialis are potentially valuable foraging grounds for the little auks 72 , 80 , in contrast to the intensively Atlantified area of Kongsfjorden, where C . glacialis is extremely scarce.…”

The Little Auk Alle alle: an ecological indicator of a changing Arctic and a model organism

“…Whilst foraging under water, Little Auks capture copepods by visually guided suction feeding, achieved through an extension of their gular pouch (Enstipp et al 2018). Thus, the highest densities of foraging Little Auks in the vicinity of one of the largest breeding aggregations in Svalbard were observed in areas with abundant C. glacialis and high water transparency (Stempniewicz et al 2013(Stempniewicz et al , 2021. The maximum depth (mean ± SD) recorded during foraging dives by Little Auks from colonies on Spitsbergen and on Greenland was 9.9 ± 6.9 m, whilst the maximum depth attained by any bird was 37.8 m (Karnovsky et al 2011).…”